(1) Technical Field
This invention relates to the field of disk drives, in particular, to a trace suspension assembly that accommodates the smaller, magnetoresistive heads and their flying attitude with respect to the surface of a rotating disk.
(2) Description of the Prior Art
The following five patents relate to methods dealing with static attitude compensation of head suspension assemblies.
U.S. Pat. No. 5,636,089 issued Jun. 3, 1997 to Ryan A. Jurgenson et al, discloses a method and apparatus to reduce or eliminate static pitch offset error and static roll offset error by adding a dimple to a configured flexure tongue. The dimple is spaced longitudinally along the axis of a head suspension assembly from a static offset error correction protuberance, which is used for engaging and applying a load to a head slider mounted on the flexure tongue.
U.S. Pat. No. 5,608,590 issued Mar. 4, 1997 to David A Ziegler et al, discloses a gimbal flexure with static compensation and load point integral etched features.
U.S. Pat. No. 5,321,568 issued Jun. 14, 1994 to Shahab Hatam-Tabrizi, discloses a method and apparatus to improve pitch and roll characteristics by incorporating a bump or dimple disposed to contact both the top surface of the slider and the load beam so that, in effect, the slider is continuously pressed against the contact point formed by the dimple. Additionally, an elastomeric material is applied between the load beam and flexure to prevent the slider from sliding to an off-track position while damping any mechanical resonances on the head suspension assembly.
U.S. Pat. No. 5,282,103 issued Jan. 25, 1994 to Michael R. Hatch et al, discloses a magnetic head suspension assembly fabricated with an integral load beam and flexure.
U.S. Pat. No. 5,237,475 issued Aug. 17, 1993 to Toshio Kazama et al, discloses a magnetic head suspension assembly, with an adapter, for photo-magnetic recording.
In a hard disk drive, a head slider is positioned by a head suspension assembly (HSA) over a magnetic disk to facilitate reading and writing of information to the disk. Across the spectrum from network servers to personal computers and desktop workstations to notebook systems, the capacity demands placed on hard disk drives are increasing faster than ever before. Because lower costs per megabyte are also disired, the conventional method of adding disks and heads is less and less appropriate. Instead, the primary engineering challange is to continue increasing areal densities, or bits of data per square inch of disk surface.
To date, drive manufacturers have successfully doubled capacities every 12 to 18 months by increasing areal density. Pushing areal densities higher results in smaller recorded patterns on the disk, hence, weaker signals generated by the read head. The consensus then, leads to a major transition in head technology in order to continue the swift pace of areal density improvements seen today. This transition from inductive head technology, used since the first disk drive was introduced to the new, magnetoresistive head technology (MR)! is necessary if magnetic random access storage is to remain the storage medium of choice over the course of the next decade. Laboratory tests have demonstrated that MR heads can deliver four times the areal densities possible with thin film inductive heads. MR technology allows continued reductions in the cost of stored data and has several advantages over thin film inductive heads, including separate read and write elements, high signal output, low noise and velocity independent output. However, a MR head has more leads than an inductive head.
The constituent elements of standard HSAs include a swage plate, a resilient zone, a load beam, a flexure and a head slider having a top, bottom and side surfaces. Along the far side surface, a thin film transducer is attached to the head slider so that information can be written and read from the rotating magnetic disk. The swage plate is positioned at a proximal end of the load beam, adjacent to the resilient zone and is mounted to the suspension by means of a boss and by laser welding. The swage plate provides stiffness to the rear mount section and is configured for mounting the load beam to an actuator arm of a disk drive. The flexure is positioned at a distal end of the load beam. Mounted to the flexure is a head slider with a read/write orientation with respect to an associated disk.
As the track density of hard disk drives increase, more and more attention must be paid to the design of the suspension spring, since its static attitudes and other dynamic factors limit the track density that can be achieved. In recent years, the trend in suspension design has been toward smaller suspensions and much research and development work is going on in the areas of suspension design, integration of electrical wires from the head on the suspension, and optimization of suspension design to reduce sway modes and undesirable suspension resonances.
Preload, also known as gram load, and static attitudes are crucial parameters to all suspensions used in a disk drive. More importantly, static attitudes are especially critical as the slider becomes smaller as they impart a moment on the slider. The moment must be balanced by an air bearing lift force. As the slider gets smaller, the lever arm also gets smaller, hence, the reacting lift forces becomes greater. Consequently, the effect of static attitudes on the slider's flying attitude becomes greater.
The smaller, trace suspension assembly(TSA), is extremely sensitive to static attitude excursions. The TSA is wireless. Electrical connection is made by attaching gold balls between the slider and suspension. This process causes unwanted and unpredicable change in the static attitudes, by two distinct mechanisms. First, the slider must be held firmly for the gold ball bond. During the bonding process, the holding fixture makes contact with the thin suspension and flexure causing deformation. Secondly, the trace deforms when the gold balls are ultrasonically bonded. Studies have shown that pitch static attitude greatly influences slider fly height variation.
Previously, preload adjustment was done on the suspension instead of the flexure, and performed prior to its static attitude adjustment. Preload adjustment was done by wrapping the suspension around a mandrel while heating the resilient zone of the load beam using an infra-red lamp. Only recently have tools for static attitude adjustment been made available. Pitch static adjustment is done by bending the resilient zone.
As pertaining to a TSA, roll static attitude is coincident with the longitudinal axis of the TSA. The value of roll-static attitude is measured, often optically, when the suspension is lifted so that the plane of the flexure tongue is in a predetermined height differential with respect to the plane of the swage plate. If the flexure is bent, the values measured on either side will not be the same. Thus, when the attached trace head is in a flying attitude to the associated disk surface, an effected force is needed to twist the tongue back into a planar parallel alignment to the disk.
Pitch static attitude has its axis perpendicular to the longitudinal axis of the TSA, and thus to the roll axis. The value of the pitch static attitude is measured often optically, when the suspension is lifted against preload, such that the plane of the flexure tongue is a predetermined height differential with respect to the plane of the swage plate. If the flexure is bent, the values measured on either side will not be the same. Thus, when the attached trace head is in a flying attitude to the associated disk surface, an effected force is needed to twist the tongue back into a planar parallel alignment to the disk. It will of course be understood that under actual conditions, the flexure may need to be effectively twisted with respect to both axis, to achieve alignment about both the pitch and roll axis.
These pitch and roll conditions can also be referred to in terms of static attitude at the flexure/slider interface and, in terms of the pitch and roll stiffness of the flexure. In an actual disk drive, pitch and roll attitude produce unfavorable forces between the air bearing surface of the trace head and disk, affecting the flying height of the trace head above the disk, resulting in deviations from optimum head/disk interface separation.
The disk drive industry has been trying to reduce static attitude errors for years by reverse bending of its load beam. This is undesirable because the deviation often arises from the flexure. Compensating one deviation with another can cause side effects such as altered suspension-to-disk clearance and change in the vibration modes. The present invention adjusts the static attitude by deforming the flexure, thus preserving the load beam profile.